This invention relates to an improved transmission. It may be considered an improvement on the hydromechanical transmission described in U.S. Pat. No. 3,888,139 which issued June 10, 1975, to Elias Orshansky, Jr., or an improvement on our co-pending patent application, Ser. No. 787,851, filed Apr. 15, 1977.
The transmission of U.S. Pat. No. 3,888,139, that of Application Ser. No. 787,851, and the transmission of the present invention each provide a hydromechanical infinitely variable transmission. Each provides for improved utilization of vehicle engine power by enabling the engine to operate within a narrow speed range which has been optimized for minimum emissions, maximum fuel economy and maximum power, regardless of vehicle operating conditions.
In U.S. Pat. No. 3,888,139 the hydraulic units used as a speed-varying means were driven by gears from either the input or the reaction or both. The transmission of Application Ser. No. 785,851 and of the present invention eliminate those gears, four gears altogether, and their bearings, in order to reduce the size and weight of the transmission and to reduce the cost of the transmission.
It is also an object to provide a transmission which can weigh less than conventional transmissions.
The transmission of this invention and that of Application Ser. No. 787,851 have a concentric or coaxial construction and an entirely different hydrostatic start from the transmission of U.S. Pat. No. 3,888,139, in order to provide reduction in the number of parts, the size, the weight, and also the cost of the transmission.
In order to avoid having to use the extra gears which connected the planetary assemblies to the hydraulic units in U.S. Pat. No. 3,888,139, the hydraulic units in Application Ser. No. 787,851 and in the present invention may be especially designed to be installed in line with the planetary assemblies without a separate gear drive. This considerably reduces power losses, size, weight, and cost.
The present invention offers the opportunity for improved clutch construction, especially as regards oil supplies to the clutches, where only a few small-diameter seals are used.
In Application Ser. No. 787,851, all three sun gears are on a common shaft in driving relation with the hydraulic module, whereas in the present invention only two of the sun gears are on such a common shaft; and the third sun gear is mounted on the output shaft. Both inventions employ a releasable brake to hold the first planetary assembly's carrier stationary in a hydrostatic mode, and both of them release the brake for two succeeding hydromechanical ranges; however, in the former application both succeeding stages involved clutches engaging the output shaft, whereas in the present invention, the third or high-speed range clutches the input shaft to the third carrier, which then drives the output shaft through the third sun gear.
Since the high-range final output drive is through a sun gear, planet gear speeds and pitch line velocities are low. Consequently, bearing life is improved. Also, the noise levels in the high range can be kept low.
Furthermore, the first planetary assembly, to which the brake is attached, is of simple construction and is easily packaged.
A conventional torque converter transmission or a conventional manual transmission requires the imposition of many compromises upon the engine, because it must provide adequate performance over a wide range of torque and speed. The practice of most vehicle manufacturers of providing a selection of optional axle ratios for the vehicle is only one of the many attempts which have been made to reduce the compromise for any given application.
The infinitely variable transmission of this invention enables the engine to be operated at all times in a speed range in which it is capable of producing rated power. Therefore, vehicle performance in any given application can be maintained or even improved while utilizing a smaller engine. In contrast, infinitely variable transmissions of the pure hydrostatic type are limited to applications where significant power losses can be tolerated in return for the benefits of improved transmission control.
Hydromechanical transmissions offer the control benefits of hydrostatic transmissions, and, since only a portion of the engine power is transmitted by the hydraulic units, they provide a means for removing the performance barrier of excessive power losses. The extent to which any hydromechanical transmission can accomplish this is a function of the percentage of power which must be transmitted hydraulically.
The new transmission hereof can transmit high horsepower over a wide range of output speed variation at a constant input speed and horsepower. It differs from the previous transmission in its ability to transmit power over a wide range with a minimum of transmitted hydraulic horsepower, and a minimum of installed hydraulic horsepower. It also provides full engine braking over its entire range of operation.
The invention avoids the pitfalls of excessive complexity, speeds, or loads in the gear train. Maximun reliability and minimum cost have been obtained by utilizing standard commercial hydraulic unit design practice in which the units are operated totally within their long-life rated conditions of speed and power. In addition, the clutches can utilize the same low-cost paper elements presently employed in high-production automobile torque converter transmission. For a comparable power rating, a smaller number of elements than in a torque converter power shift transmission can be utilized, because at all shift points the clutch elements are virtually synchronous. The number of elements is, therefore, a function not of their thermal capacity, but of their steady-state torque capacity.
This new transmission is valuable for use in passenger and competition cars, highway and off-highway trucks, buses, agricultural and construction equipment, military vehicles, and industrial drives and machine tools.
With this invention it is possible to design transmissions having an extremely wide range of speed and torque variation at full power. This is required in construction and off-highway equipment, for example, where torque multiplication of the order of 18:1 and 24:1 may be encountered. Machine tool drives may require even wider ranges, and they are possible.
The use of this transmission in a piston-engine vehicle enables reduction of exhaust emissions and improvement in the specific fuel consumption by programming the engine to operate within its optimum range under all road conditions without regard to transmission torque output requirements. Both hydrocarbon and nitrogen oxide emissions can be minimized by optimizing the engine for operation in a specific narrow range. In addition, a smaller engine may be utilized for any application, as the transmission enables full engine power to be developed at any vehicle speed except for the lower speeds where the vehicle is traction limited. It is particularly desirable to operate turbocharged diesel engines in a narrow range of speed.
Rotary combustion engines can use this new transmission with the same advantages as for piston engines. The benefit in reduction of hydrocarbon emissions is therefore of a much greater magnitude, however, due to the high rate of change in emission characteristics for rotary combustion engines with respect to engine speed.
Gas turbines would also be benefited significantly by this invention. Manufacturing cost is a major drawback in producing a turbine today. This, to a large degree, is a function of the complexity required in the design of a turbine for use under the varying torque and speed conditions of a road vehicle. With the hydromechanical transmission of this invention, the turbine can be programmed to operate only under those conditions during which it is most efficient. Therefore, a single-shaft turbine becomes feasible, as it is more economical to manufacture than the two-shaft design normally proposed for vehicle application. Since constant-speed operation is feasible, the problems in connection with the throttle response time of a turbine do not arise. Because there is an infinite variation in speed and torque in the transmission, and no interruption of power flow occurs at any time, the turbine is never unloaded.